quartz是一个定时任务，如果是自己实现定时任务会怎么做呢？正常的做法都会使用一个生产者多个消费者模式，生产者获取任务交给消费者去消费。消费者交给jdk的线程池去管理。在阅读源码的时候，首先不去看源码，而是想想如果自己去实现这样的业务，会怎么做，然后再去分析代码能够起到事半功倍的效果。
分析quartz源码后，quartz确实是采用的一个生产者多个消费者模式，只不过是一个调度器(Scheduler)一个生产者线程，但使用spring boot基本都是一个调度器，所以可以说是一个生产者。线程池不是采用的jdk线程池，而是自己实现了一套线程池，原理差不多。quartz生产者线程是QuartzSchedulerThread，消费者线程是WorkerThread，WorkerThread是SimpleThreadPool的内部类。
1. QuartzSchedulerThread线程
分析线程，要分析两个事情，一是什么时候启动的，二是run方法做了什么,也就是分析Thread的start方法和run方法
1.1 启动
在quartz初始化一节中写到，在创建Scheduler的时候会创建一个QuartzScheduler对象，构建QuartzScheduler对象的时候会启动QuartzSchedulerThread线程。代码如下:
public QuartzScheduler(QuartzSchedulerResources resources, long idleWaitTime, @Deprecated long dbRetryInterval)
throws SchedulerException {
...
this.schedThread = new QuartzSchedulerThread(this, resources);
ThreadExecutor schedThreadExecutor = resources.getThreadExecutor();
schedThreadExecutor.execute(this.schedThread);
...
}
ThreadExecutor可以在配置文件指定 ，默认是DefaultThreadExecutor。
1.2 run方法
@Override
public void run() {
int acquiresFailed = 0;
//---------------1. 判断调度器是否中断---------------------------
while (!halted.get()) {
try {
// check if we're supposed to pause...
synchronized (sigLock) {
while (paused && !halted.get()) {
try {
// wait until togglePause(false) is called...
sigLock.wait(1000L);
} catch (InterruptedException ignore) {
}
// reset failure counter when paused, so that we don't
// wait again after unpausing
acquiresFailed = 0;
}
if (halted.get()) {
break;
}
}
// wait a bit, if reading from job store is consistently
// failing (e.g. DB is down or restarting)..
if (acquiresFailed > 1) {
try {
long delay = computeDelayForRepeatedErrors(qsRsrcs.getJobStore(), acquiresFailed);
Thread.sleep(delay);
} catch (Exception ignore) {
}
}
//--------------2. 判读消费者的可用线程是否大于0，一直会返回true--------------------------
int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();
if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...
List triggers;
long now = System.currentTimeMillis();
clearSignaledSchedulingChange();
try {
//--------------3. 获取将要执行的触发器-----------------------------
triggers = qsRsrcs.getJobStore().acquireNextTriggers(
now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow());
acquiresFailed = 0;
if (log.isDebugEnabled())
log.debug("batch acquisition of " + (triggers == null ? 0 : triggers.size()) + " triggers");
} catch (JobPersistenceException jpe) {
if (acquiresFailed == 0) {
qs.notifySchedulerListenersError(
"An error occurred while scanning for the next triggers to fire.",
jpe);
}
if (acquiresFailed < Integer.MAX_VALUE)
acquiresFailed++;
continue;
} catch (RuntimeException e) {
if (acquiresFailed == 0) {
getLog().error("quartzSchedulerThreadLoop: RuntimeException "
+e.getMessage(), e);
}
if (acquiresFailed < Integer.MAX_VALUE)
acquiresFailed++;
continue;
}
//4. 取出第一个触发器，判断是否达到触发时间
if (triggers != null && !triggers.isEmpty()) {
now = System.currentTimeMillis();
long triggerTime = triggers.get(0).getNextFireTime().getTime();
long timeUntilTrigger = triggerTime - now;
while(timeUntilTrigger > 2) {
synchronized (sigLock) {
if (halted.get()) {
break;
}
if (!isCandidateNewTimeEarlierWithinReason(triggerTime, false)) {
try {
// we could have blocked a long while
// on 'synchronize', so we must recompute
now = System.currentTimeMillis();
timeUntilTrigger = triggerTime - now;
if(timeUntilTrigger >= 1)
sigLock.wait(timeUntilTrigger);
} catch (InterruptedException ignore) {
}
}
}
if(releaseIfScheduleChangedSignificantly(triggers, triggerTime)) {
break;
}
now = System.currentTimeMillis();
timeUntilTrigger = triggerTime - now;
}
// this happens if releaseIfScheduleChangedSignificantly decided to release triggers
if(triggers.isEmpty())
continue;
//---------5. 将触发器封装成TriggerFiredResult去执行-----------------------------------
// set triggers to 'executing'
List bndles = new ArrayList();
boolean goAhead = true;
synchronized(sigLock) {
goAhead = !halted.get();
}
if(goAhead) {
try {
List res = qsRsrcs.getJobStore().triggersFired(triggers);
if(res != null)
bndles = res;
} catch (SchedulerException se) {
qs.notifySchedulerListenersError(
"An error occurred while firing triggers '"
+ triggers + "'", se);
//QTZ-179 : a problem occurred interacting with the triggers from the db
//we release them and loop again
for (int i = 0; i < triggers.size(); i++) {
qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
}
continue;
}
}
for (int i = 0; i < bndles.size(); i++) {
TriggerFiredResult result = bndles.get(i);
TriggerFiredBundle bndle = result.getTriggerFiredBundle();
Exception exception = result.getException();
if (exception instanceof RuntimeException) {
getLog().error("RuntimeException while firing trigger " + triggers.get(i), exception);
qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
continue;
}
// it's possible to get 'null' if the triggers was paused,
// blocked, or other similar occurrences that prevent it being
// fired at this time... or if the scheduler was shutdown (halted)
if (bndle == null) {
qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
continue;
}
//------------6. 创建JobRunShell-----------------
JobRunShell shell = null;
try {
shell = qsRsrcs.getJobRunShellFactory().createJobRunShell(bndle);
shell.initialize(qs);
} catch (SchedulerException se) {
qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
continue;
}
//---------------7. 任务交给消费者消费---------------------------
if (qsRsrcs.getThreadPool().runInThread(shell) == false) {
// this case should never happen, as it is indicative of the
// scheduler being shutdown or a bug in the thread pool or
// a thread pool being used concurrently - which the docs
// say not to do...
getLog().error("ThreadPool.runInThread() return false!");
qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
}
}
continue; // while (!halted)
}
} else { // if(availThreadCount > 0)
// should never happen, if threadPool.blockForAvailableThreads() follows contract
continue; // while (!halted)
}
long now = System.currentTimeMillis();
long waitTime = now + getRandomizedIdleWaitTime();
long timeUntilContinue = waitTime - now;
synchronized(sigLock) {
try {
if(!halted.get()) {
// QTZ-336 A job might have been completed in the mean time and we might have
// missed the scheduled changed signal by not waiting for the notify() yet
// Check that before waiting for too long in case this very job needs to be
// scheduled very soon
if (!isScheduleChanged()) {
sigLock.wait(timeUntilContinue);
}
}
} catch (InterruptedException ignore) {
}
}
} catch(RuntimeException re) {
getLog().error("Runtime error occurred in main trigger firing loop.", re);
}
} // while (!halted)
// drop references to scheduler stuff to aid garbage collection...
qs = null;
qsRsrcs = null;
}
QuartzSchedulerThread线程的run方法很长，也很复杂，需要分成几段去看，在代码中我分了段并写了注释。主要分为以下几个步骤：
- 判断调度器是否中断
- 判读消费者的可用线程是否大于0，一直会返回true，blockForAvailableThreads方法会一直循环，知道大于0时才会返回
- 获取将要执行的触发器，这里会查询将来30s过去60s的触发器，为嘛会查询过去的，有时消费者线程不足导致触发器没有执行，就再执行一次。
- 取出第一个触发器，判断是否达到触发时间，查询出来的触发器已经排序了，所以第一个到时间了，其他的也会执行
- 将触发器封装成TriggerFiredResult去执行
- 把触发器封装成JobRunShell，JobRunShell实现了Runnable接口
- 交给消费者去消费
整体流程图，图片来源于https://segmentfault.com/a/1190000015492260
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2. WorkerThread线程
由上节知道，生产者最终时交给消费者线程池的runInThread去执行任务，首先看SimpleThreadPool的runInThread的方法
public boolean runInThread(Runnable runnable) {
if (runnable == null) {
return false;
}
synchronized (nextRunnableLock) {
handoffPending = true;
// Wait until a worker thread is available
while ((availWorkers.size() < 1) && !isShutdown) {
try {
nextRunnableLock.wait(500);
} catch (InterruptedException ignore) {
}
}
if (!isShutdown) {
WorkerThread wt = (WorkerThread)availWorkers.removeFirst();
busyWorkers.add(wt);
wt.run(runnable);
} else {
// If the thread pool is going down, execute the Runnable
// within a new additional worker thread (no thread from the pool).
WorkerThread wt = new WorkerThread(this, threadGroup,
"WorkerThread-LastJob", prio, isMakeThreadsDaemons(), runnable);
busyWorkers.add(wt);
workers.add(wt);
wt.start();
}
nextRunnableLock.notifyAll();
handoffPending = false;
}
return true;
}
runInThread方法主要是对线程池的操作，从可用线程中获取线程，把获取的线程加入到忙碌的线程列表中。然后再看WorkerThread的run方法：
@Override
public void run() {
boolean ran = false;
while (run.get()) {
try {
synchronized(lock) {
while (runnable == null && run.get()) {
lock.wait(500);
}
if (runnable != null) {
ran = true;
runnable.run();
}
}
} catch (InterruptedException unblock) {
// do nothing (loop will terminate if shutdown() was called
try {
getLog().error("Worker thread was interrupt()'ed.", unblock);
} catch(Exception e) {
// ignore to help with a tomcat glitch
}
} catch (Throwable exceptionInRunnable) {
try {
getLog().error("Error while executing the Runnable: ",
exceptionInRunnable);
} catch(Exception e) {
// ignore to help with a tomcat glitch
}
} finally {
synchronized(lock) {
runnable = null;
}
// repair the thread in case the runnable mucked it up...
if(getPriority() != tp.getThreadPriority()) {
setPriority(tp.getThreadPriority());
}
if (runOnce) {
run.set(false);
clearFromBusyWorkersList(this);
} else if(ran) {
ran = false;
makeAvailable(this);
}
}
}
//if (log.isDebugEnabled())
try {
getLog().debug("WorkerThread is shut down.");
} catch(Exception e) {
// ignore to help with a tomcat glitch
}
}
}
WorkerThread的run方法代码比较多，大量的try-catch和日志代码，把这些代码去掉，真正就一句代码 runnable.run();runnable指的是JobRunShell，继续看JobRunShell的run方法
public void run() {
qs.addInternalSchedulerListener(this);
try {
OperableTrigger trigger = (OperableTrigger) jec.getTrigger();
JobDetail jobDetail = jec.getJobDetail();
do {
JobExecutionException jobExEx = null;
Job job = jec.getJobInstance();
//1. 空方法，交给子类实现
try {
begin();
} catch (SchedulerException se) {
qs.notifySchedulerListenersError("Error executing Job ("
+ jec.getJobDetail().getKey()
+ ": couldn't begin execution.", se);
break;
}
//2. 通知job和trigger监听器，任务开始执行
// notify job & trigger listeners...
try {
if (!notifyListenersBeginning(jec)) {
break;
}
} catch(VetoedException ve) {
try {
CompletedExecutionInstruction instCode = trigger.executionComplete(jec, null);
qs.notifyJobStoreJobVetoed(trigger, jobDetail, instCode);
// QTZ-205
// Even if trigger got vetoed, we still needs to check to see if it's the trigger's finalized run or not.
if (jec.getTrigger().getNextFireTime() == null) {
qs.notifySchedulerListenersFinalized(jec.getTrigger());
}
complete(true);
} catch (SchedulerException se) {
qs.notifySchedulerListenersError("Error during veto of Job ("
+ jec.getJobDetail().getKey()
+ ": couldn't finalize execution.", se);
}
break;
}
//3. 执行任务
long startTime = System.currentTimeMillis();
long endTime = startTime;
// execute the job
try {
log.debug("Calling execute on job " + jobDetail.getKey());
job.execute(jec);
endTime = System.currentTimeMillis();
} catch (JobExecutionException jee) {
endTime = System.currentTimeMillis();
jobExEx = jee;
getLog().info("Job " + jobDetail.getKey() +
" threw a JobExecutionException: ", jobExEx);
} catch (Throwable e) {
endTime = System.currentTimeMillis();
getLog().error("Job " + jobDetail.getKey() +
" threw an unhandled Exception: ", e);
SchedulerException se = new SchedulerException(
"Job threw an unhandled exception.", e);
qs.notifySchedulerListenersError("Job ("
+ jec.getJobDetail().getKey()
+ " threw an exception.", se);
jobExEx = new JobExecutionException(se, false);
}
jec.setJobRunTime(endTime - startTime);
//4. 通知job和trigger监听器任务执行完成
// notify all job listeners
if (!notifyJobListenersComplete(jec, jobExEx)) {
break;
}
CompletedExecutionInstruction instCode = CompletedExecutionInstruction.NOOP;
// update the trigger
try {
instCode = trigger.executionComplete(jec, jobExEx);
} catch (Exception e) {
// If this happens, there's a bug in the trigger...
SchedulerException se = new SchedulerException(
"Trigger threw an unhandled exception.", e);
qs.notifySchedulerListenersError(
"Please report this error to the Quartz developers.",
se);
}
// notify all trigger listeners
if (!notifyTriggerListenersComplete(jec, instCode)) {
break;
}
// update job/trigger or re-execute job
if (instCode == CompletedExecutionInstruction.RE_EXECUTE_JOB) {
jec.incrementRefireCount();
try {
complete(false);
} catch (SchedulerException se) {
qs.notifySchedulerListenersError("Error executing Job ("
+ jec.getJobDetail().getKey()
+ ": couldn't finalize execution.", se);
}
continue;
}
//5. 空方法，交给子类完成，
try {
complete(true);
} catch (SchedulerException se) {
qs.notifySchedulerListenersError("Error executing Job ("
+ jec.getJobDetail().getKey()
+ ": couldn't finalize execution.", se);
continue;
}
qs.notifyJobStoreJobComplete(trigger, jobDetail, instCode);
break;
} while (true);
} finally {
qs.removeInternalSchedulerListener(this);
}
}
执行流程：
- 空方法，交给子类实现，方便扩展，任务执行开始
- 通知job和trigger监听器，任务开始执行
- 执行任务
- 通知job和trigger监听器任务执行完成
- 空方法，交给子类完成，任务执行完成